Field of the Invention
The present invention relates to an immersion microscope objective, and a microscope using the same.
Description of the Related Art
Recently, in research in biology and genetics, there is a desire and demand to perform fluorescence observation on a thick and live biological specimen with high resolving power. To meet this demand, a microscope objective is required to have a large numerical aperture (high NA) and high magnification.
The microscope objective of this kind is often used in a confocal laser scanning microscope. A confocal laser scanning microscope has a very small depth of focus, so it can obtain a sectioning image of a specimen. In order to obtain an accurate sectioning image, the microscope objective is required to have high flatness of a field.
An immersion microscope objective is the microscope objective that can satisfy such requirements. In an immersion microscope objective, there is an immersion liquid between the immersion microscope objective and a specimen. Thus, when the immersion microscope objective is used to observe a deep portion of a biological specimen, spherical aberration may occur, depending on the type of the immersion liquid used, because of the difference between the refractive index (1.33 to 1.45) of the biological specimen and the refractive index of the immersion liquid. In order to reduce such spherical aberration, it is desirable that the biological specimen and the immersion liquid have similar refractive indices.
Specifically, as an immersion liquid, the following are desirable: water (refractive index: 1.33), culture solution (refractive index: 1.33), silicone oil (refractive index: 1.40), and a mixture of glycerin and water (refractive index: 1.33 to 1.47). Further, it is preferable that an immersion microscope objective also has its aberrations favorably corrected for these immersion liquids.
Furthermore, the spherical aberration varies depending on the position being observed (i.e. the depth from the surface of the biological specimen). Therefore, it is desirable that the immersion microscope objective is provided with a correction collar, which enables correction of the spherical aberration.
As an immersion microscope objective having a large numerical aperture, an immersion microscope objective disclosed in Japanese Patent Application Laid-Open No. 2008-170969 is available. In the immersion microscope objective disclosed in Japanese Patent Application Laid-Open No. 2008-170969, the magnification and numerical aperture are 60× and 1.4, respectively, in the case of an oil immersion microscope objective, and 60× and 1.3, respectively, in the case of a silicone immersion microscope objective.